When producing soft paper, such as toilet paper, household paper, napkins and similar hygiene products, the softness and absorbency of the paper is usually achieved by a so called creping method. In this method, the still wet fibre layer/web produced in the forming of the paper is led onto a drying cylinder and the finally dried or partially dried web is scraped off and pulled off on an exit side of the cylinder, after which it is led on to subsequent optional additional drying and/or reeling. In the line of trade, such drying cylinders are called “Yankee cylinders”. These cylinders are characterised by their large diameter which is between 3 and 5 metres. The drying of the paper web takes place by the contact with the hot surface that usually is heated by internal supply of steam and by external supply of hot air.
Hence, the so called creping takes place in the above mentioned web transfer (scraping off). In this process, the running web is “scraped off” from the cylinder by a so called counter blade that with a certain pressure bears against the cylindrical surface. By the running web meeting the blunt surface of said blade, a micro-crinkling of the web/paper takes place. This micro-crinkling that accordingly is called creping, increases the thickness and the softness of the paper. A prerequisite for creping to take place is that the running web exhibits a certain adhesion to the cylindrical surface. This adhesion can be natural, by the paper not being completely dried, or by the fibre composition of the paper containing components that adhere to the cylindrical surface. A common way of achieving the desired adhesion is to externally supply adhesive agents to the cylindrical surface. Usually, this takes place by spraying the adhesive substance at low concentration onto the cylindrical surface.
Hence, the active machine component in the creping process is a counter blade, a so called creping doctor that with a pressure bears against the cylindrical surface and the blunt surface of which scraping off and micro-crinkling the paper. The creping doctor is arranged in a holder that has the following main functions:                Achieving a controllable bearing pressure for the creping doctor against the cylindrical surface.        Enabling engaging and disengaging of the creping doctor.        Enabling fast exchanging of the creping doctor.        
The contact between the creping doctor and the cylindrical surface results in wear of the creping doctor as well as the cylindrical surface. This results in negative process consequences in the form of wear. For the creping doctor, the consequences of the wear is that it has to be exchanged, which besides the cost of the creping doctor means considerable costs for production loss in connection with the exchanging. For the cylindrical surface, the consequences of the wear is that every now and then the surface must be re-ground, which is costly. Since the cylinder is a pressure vessel, the cylinder must also have a certain jacket thickness. This means that the cylinder must be redressed with a new wearing surface after a certain number of re-grindings. Another consequence of the creping doctor wear is that the quality of the crepe paper changes with the level of wear.
In order to keep down the wear it is important to maintain a pressure that is as small as possible between the tip of the creping doctor and the cylindrical surface. A certain minimum pressure must however be maintained in order to prevent the paper web, or parts of the paper web, from passing between the creping doctor and the cylindrical surface, which otherwise results in web break.
The most common way of achieving a desired creping doctor pressure is to rotate the holder about its axis of suspension. Due to the rotation, the creping doctor will bend more or less and thereby it will apply a resilient pressure against the cylindrical surface. The drawback of this solution is that the bearing pressure cannot be increased with the wear since the creping doctor is flexible and its bending increases with the pressure, which in turn results in the contact surface against the cylinder at a certain pressure level forming an open wedge, which in turn increases the risk of the web getting caught and thus causing web break.
Said drawback can be eliminated by a device that is described in Swedish patent no. SE 505,667. This device enables the pressure to be changed without changing the contact angle of the creping doctor against the cylindrical surface. This is achieved by separate pressure means that act near the tip of the creping doctor, whereby the creping doctor is not bent in connection with the pressure change. Thereby, the time intervals between changes of the creping doctor can be prolonged, i.e. its lifespan increases.
The lifespan of the creping doctor can also be increased by the tip of the doctor and the contact surface against the cylinder being coated with a material that is harder than the actual basal body of the creping doctor. An example of this solution is described in GB 2,128,551. The problem with this solution is that it is easier for the harder material to damage the cylindrical surface, such as by wear.
In order to decrease the wear of the cylindrical surface, the substance that increases the adhesion of the paper web against the cylindrical surface can be combined with a substance that builds up a layer on the cylindrical surface. Hereby, the tip of the creping doctor will “scrape” in the built-up layer instead of “scraping” against the cylindrical surface. The drawback of this method is among other things a high chemicals consumption and impaired heat transport through the cylinder and that chemical residues are mixed into the paper.
Although the running times for the creping doctors can be increased by the above mentioned methods, the creping doctor must nevertheless be exchanged after production intervals of more or less length. It has been tried to diminish this problem by continuously feeding a traditional long creping doctor in its longitudinal direction. The method is described in U.S. Pat. No. 4,691,406. Some, of several, problems that have prevented the method from establishing on the market is that the construction requires costly maintenance, that the adjustment possibilities are limited, that the method requires large space on both sides of the machine, and that the doctor blade consumption is high because the feeding speed needs to be high enough for the difference in wear on the incoming and exiting sides not to result in quality differences between the two sides.